The invention relates to siloxane compositions which are useful as traction fluids in traction drive systems subject to varied operating temperature and pressure conditions.
Certain hydrocarbon oils and organosilicone compounds have been found to be useful in a variety of engineering applications, including traction fluids for traction drive systems. Most current toroidalxe2x80x94continuously variable transmission (T-CVT) traction fluids are hydrocarbon molecules based primarily on dimers of the same or two different monomers. They possess saturated rings structures such as cyclohexane, alkylcyclohexane, bicycloheptane or bicyclooctane. Traction is broadly defined as the adhesive friction of a body on a surface on which it moves. A traction drive is a device in which torque is transmitted from an input element to an output element through nominal point or line contact typically with a rolling action by virtue of the traction between the contacting elements.
While traction elements are commonly spoken of as being in contact, it is generally accepted that a fluid film is present therebetween. Almost all traction drives require these fluids to remove heat, to prevent wear at the contact surfaces and to lubricate bearings and other moving parts associated with the drive. Thus, instead of metal to metal rolling contact there is a film of fluid introduced into the contact zone and interposed between the metal elements. High pressures and high shear conditions are found in this area of contact between the roller elements and so the nature of this fluid determines to a large extent the limits of performance and the capacity of the drive. It is through the traction fluid""s resistance to shear that the torque transmitting ability of a given fluid arises. The torque transmitting ability of a fluid, and thus its suitability as a traction fluid, is measured by and is directly related to its traction coefficient at varying temperatures. In addition to a fluid""s torque transmitting ability, its ability to protect against wear is also important.
The inventors have now determined that certain siloxane compositions have traction coefficients and anti-wear properties that make them useful as traction fluids at varied temperatures. An object of the invention is to provide traction fluids useful for low temperature applications. Another object of the invention is to provide traction fluids useful for high temperature applications. Another object of the invention is to provide traction fluids having improved anti-wear properties.
This invention relates to siloxane compositions which are useful as traction fluids in traction drive systems which are subject to varied operating temperature conditions. Specific siloxane compositions included contain units of formulae
(I) (R3SiO1/2)(RSiO3/2)(SiO4/2),
(II) (R3SiO1/2)(RSiO3/2),
(III) (R3SiO1/2)(SiO4/2),
(IV) (R3SiO1/2)(R2SiO2/2)(RSiO3/2),
(V) (R3SiO1/2)(R2SiO2/2), and
(VI) (R2SiO2/2)a 
in varying mole percents, where a is an integer ranging from 3 to 20 and each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms.
A method for transmitting torque in a traction drive system having at least two relatively rotatable members in a torque transmitting relationship comprising disposing on the tractive surfaces of the members a traction fluid comprising at least one siloxane composition chosen from
(I) 33 to 80 mole percent units of formula (R3SiO1/2), 0.2 to 66.8 mole percent units of formula (RSiO3/2), and 66.8 to 0.2 mole percent units of formula (SiO4/2) having a viscosity of from 1.0 to 50,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl;
(II) 33 to 75 mole percent units of formula (R3SiO1/2) and 67 to 25 mole percent units of formula (RSiO3/2) having a viscosity of from 2.0 to 20,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl;
(III) 33 to 80 mole percent units of formula (R3SiO1/2) and 67 to 20 mole percent units of formula (SiO4/2) having a viscosity of from 1.0 to 70,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl;
(IV) 0 to 28 mole percent units of formula (R3SiO1/2), 37 to 93 mole percent units of formula (R2SiO2/2), and 6 to 56 mole percent units of formula (RSiO3/2) having a viscosity of from 5.0 to 10,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl and provided further that at least one of the R groups which is not methyl is chosen from alkyl groups comprising 7 to 18 carbon atoms and aryl groups comprising 7 to 18 carbon atoms;
(V) 1 to 100 mole percent units of formula (R3SiO1/2) and 99 to 0 mole percent units of formula (R2SiO2/2) having a viscosity of from 1.0 to 50,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl and provided further that at least one of the R groups which is not methyl is chosen from alkyl groups comprising 7 to 18 carbon atoms and aryl groups comprising 7 to 18 carbon atoms; and
(VI) cyclosiloxanes of formula (R2SiO2/2)a having a viscosity of from 2.0 to 50,000 mPaxc2x7s at 40xc2x0 C., where a is an integer ranging from 3 to 20, each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl.
The traction fluids useful in the present method comprise at least one siloxane composition chosen from (I)-(VI) described above, preferably chosen from (II), (III), (IV), (V), and (VI), and more preferably chosen from (II), (III), and (VI). The siloxane compositions described above may contain monofunctional siloxane units (M units) represented by formula (R3SiO1/2), difunctional siloxane units (D units) represented by formula (R2SiO2/2), trifunctional siloxane units (T units) represented by formula (RSiO3/2), and tetrafunctional siloxane units (Q units) represented by formula (SiO4/2).
Each R in siloxane compositions (I)-(VI) is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms. The alkyl groups of R can be linear, branched and cyclic. Examples of linear alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, decyl, and octadecyl. Examples of branched alkyl groups include isobutyl, tertiary butyl, 2-ethylhexyl, 2,4,4,6,6-pentarnethylheptyl and 2,4,4-trimethylpentyl. The cyclic groups may be attached directly to the silicon atom or attached through a divalent hydrocarbon group. Preferably, the divalent hydrocarbon group is an alkylene group. In addition, the cyclic groups may have hydrocarbon groups attached to the ring. Examples of cyclic alkyl groups include cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, 2-cyclohexylethyl, 2-cyclohexylpropyl, cyclooctyl, bicyclo (2.2.1) heptyl, bicyclo (2.2.2) octyl, methylnorbornyl, ethylnorbornyl, trimethylnorbornyl, 2-norbornylethyl, and decanyl.
The aryl groups of R may be attached directly to the silicon atom or attached through a divalent hydrocarbon group. Preferably, the divalent hydrocarbon group is an alkylene group. In addition, the aryl groups may have hydrocarbon groups attached to the aromatic ring. Examples of the aryl radicals comprising 6 to 18 carbon atoms include phenyl, benzyl, tolyl, xylyl, 2-phenyl-2-methylethyl, naphthyl, methylnaphthyl, ethylnaphthyl, 2-naphthylethyl, and 2-phenylethyl.
Preferably, each R is independently selected from linear alkyl groups comprising 1 to 8 carbon atoms, branched alkyl groups comprising 4 to 18 carbon atoms, and cyclic alkyl groups comprising 5 to 18 carbon atoms. Alternatively, each R may also be independently selected from methyl, cyclohexyl, 2,4,4-trimethylpentyl, and norbornyl.
Siloxane composition (I) contains 33 to 80 mole percent siloxane units of formula (R3SiO1/2) (M units), 0.2 to 66.8 mole percent siloxane units of formula (RSiO3/2) (T units), and 66.8 to 0.2 mole percent siloxane units of formula (SiO4/2) (Q units) having a viscosity of from 1.0 to 50,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl. Examples of R are as described above. Although siloxane composition (I) generally contains M units, T units, and Q units in each molecule, so long as it doesn""t affect the object of the invention, siloxane composition (I) may also contain difunctional siloxane units (D units) represented by formula (R2SiO2/2).
Siloxane composition (II) contains 33 to 75 mole percent siloxane units of formula (R3SiO1/2) (M units) and 67 to 25 mole percent siloxane units of formula (RSiO3/2) (T units) having a viscosity of from 2.0 to 20,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl.
Preferably, siloxane composition (II) contains 33 to 67 mole percent M units and 67 to 33 mole percent T units having a viscosity of from 5.0 to 20,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from linear alkyl groups comprising 1 to 8 carbon atoms, branched alkyl groups comprising 4 to 18 carbon atoms, and cyclic alkyl groups comprising 5 to 18 carbon atoms provided from 15 to 60 mole percent of R groups are not methyl.
More preferably, siloxane composition (11) contains 50 to 67 mole percent M units and 50 to 33 mole percent T units having a viscosity of from 5.0 to 5,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from methyl, cyclohexyl, 2,4,4-trimethylpentyl, and norbornyl provided from 18 to 57 mole percent of R groups are not methyl.
Siloxane composition (III) contains 33 to 80 mole percent units of formula (R3SiO1/2) (M units) and 67 to 20 mole percent units of formula (SiO4/2) (Q units) having a viscosity of from 1.0 to 70,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl. Although siloxane composition (III) generally contains M and Q units in each molecule, so long as it doesn""t affect the object of the invention, siloxane composition (III) may also contain difunctional siloxane units (D units) represented by formula (R2SiO2/2).
Preferably, siloxane composition (III) contains 50 to 75 mole percent M units and 50 to 25 mole percent Q units having a viscosity of from 5.0 to 50,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from linear alkyl groups comprising 1 to 8 carbon atoms, branched alkyl groups comprising 4 to 18 carbon atoms, and cyclic alkyl groups comprising 5 to 18 carbon atoms provided from 10 to 67 mole percent of R groups are not methyl.
More preferably, siloxane composition (III) contains 67.0 to 71.4 mole percent M units and 33.0 to 28.6 mole percent Q units having a viscosity of from 10.0 to 5,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from methyl, cyclohexyl, 2,4,4-trimethylpentyl, and norbornyl provided from 24 to 67 mole percent of R groups are not methyl.
Siloxane composition (IV) contains 0 to 28 mole percent units of formula (R3SiO1/2) (M units), 37 to 93 mole percent units of formula (R2SiO2/2) (D units), and 6 to 56 mole percent units of formula (RSiO3/2) (T units) having a viscosity of from 5.0 to 10,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl and provided further that at least one of the R groups which is not methyl is chosen from alkyl groups comprising 7 to 18 carbon atoms and aryl groups comprising 7 to 18 carbon atoms.
Preferably, siloxane composition (IV) contains 0.1 to 10 mole percent M units, 40 to 55 mole percent D units and 40 to 55 mole percent T units having a viscosity of from 200 to 5,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from linear alkyl groups comprising 1 to 8 carbon atoms, branched alkyl groups comprising 4 to 18 carbon atoms, and cyclic alkyl groups comprising 5 to 18 carbon atoms provided from 10 to 50 mole percent of R groups are not methyl and provided further that at least one of the R groups which is not methyl is chosen from alkyl groups comprising 7 to 18 carbon atoms.
Siloxane composition (V) contains 1 to 100 mole percent units of formula (R3SiO1/2) (M units) and 99 to 0 mole percent units of formula (R2SiO2/2) (D units) having a viscosity of from 1.0 to 50,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl and provided further that at least one of the R groups which is not methyl is chosen from alkyl groups comprising 7 to 18 carbon atoms and aryl groups comprising 7 to 18 carbon atoms.
Preferably, siloxane composition (V) contains 2.0 to 100 mole percent M units and 98 to 0 mole percent D units having a viscosity of from 2.0 to 30,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from linear alkyl groups comprising 1 to 8 carbon atoms, branched alkyl groups comprising 4 to 18 carbon atoms, and cyclic alkyl groups comprising 5 to 18 carbon atoms provided from 10 to 60 mole percent of R groups are not methyl and provided further that at least one of the R groups which is not methyl is chosen from alkyl groups comprising 7 to 18 carbon atoms.
More preferably, siloxane composition (V) contains 5.0 to 100 mole percent M units and 95 to 0 mole percent D units having a viscosity of from 3.0 to 5,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from linear alkyl groups comprising 1 to 8 carbon atoms, branched alkyl groups comprising 4 to 18 carbon atoms, and cyclic alkyl groups comprising 5 to 18 carbon atoms provided from 10 to 50 mole percent of R groups are not methyl and provided further that at least one of the R groups which is not methyl is chosen from alkyl groups comprising 7 to 18 carbon atoms.
Siloxane composition (VI) contains cyclosiloxanes of formula (R2SiO2/2)a (Da units) having a viscosity of from 2.0 to 50,000 mPaxc2x7s at 40xc2x0 C., where a is an integer ranging from 3 to 20, each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl.
Preferably, siloxane composition (VI) contains cyclosiloxanes of formula (R2SiO2/2)a having a viscosity of from 5.0 to 50,000 mPaxc2x7s at 40xc2x0 C., where a is an integer ranging from 4 to 10, each R is independently selected from linear alkyl groups comprising 1 to 8 carbon atoms, branched alkyl groups comprising 4 to 18 carbon atoms, and cyclic alkyl groups comprising 5 to 18 carbon atoms provided from 10 to 50 mole percent of R groups are not methyl.
More preferably, siloxane composition (VI) contains cyclosiloxanes of formula (R2SiO2/2)a having a viscosity of from 5.0 to 50,000 mPaxc2x7s at 40xc2x0 C., where a is an integer ranging from 4 to 10 and each R is independently selected from methyl, cyclohexyl, 2,4,4-trimethylpentyl, and norbornyl provided from 10 to 50 mole percent of R groups are not methyl.
The siloxane compositions useful in this invention may be prepared by methods well known in the art. The specific units in siloxane fluids (I)-(V) are basic silicon containing intermediates. The copolymerization of these units is generally accomplished by hydrolysis and subsequently the condensation of either chlorosilanes or alkoxysilanes. For example, siloxane fluids (I)-(V) may be prepared by the hydrolysis and condensation of appropriate amounts of RSiCl3, R2SiCl2, R3SiCl, and SiCl4 where R is as described above. A review of this process can be found in xe2x80x9cThe Chemistry and Technology of Silicones,xe2x80x9d pp. 192-198, by W. Noll (1968). When using chlorosilanes as a starting material HCl is generated as a by-product and must be neutralized or otherwise removed. One can neutralize HCl using an aqueous solution of base, such as a bicarbonate or carbonate salt of a metal such as sodium or potassium or calcium, or by repeated washing with water. Both methods may also be employed together. When made from alkoxysilanes, residual alcohol can be distilled overhead. Those skilled in the art will recognize that catalysts such as minerals, acids, and bases can be used to facilitate the hydrolysis/condensation process. A neutral solvent such as toluene may also be used to facilitate the reaction. A solvent may also be used when various reactive capping agents are used to reduce residual silanols in the siloxane fluid. The solvent may then be removed by known methods such as distillation after the siloxane fluid""s manufacture is complete.
R groups other than methyl can be added to the M, D, and T units either before the hydrolysis/condensation process or after. In either case, two principle routes are available to put these groups on the silicon. One involves the use of the corresponding chlorosilane and subjecting it to a Grignard process (Noll, pp 42-46). This is especially effective for adding aromatic groups to silicon, and has been industrially practiced for over 50 years. If it is preferred to eliminate the unsaturation from the molecule, hydrogenation of the aromatic group can be carried out as a second step. A variety of hydrogenation catalysts, such as nickel or platinum complexes, can be used to carry out the reaction.
The second process path is to add an olefin to a hydrogen function silicone material using a platinum catalyst system (Noll, pp. 50-55). Such a reaction can be carried out on the starting monomeric M, D, or T unit; or it can be carried out on a polymer or copolymer intermediate that has the correct amount of silicon hydride functionality in its structure.
Depending on the olefin employed, a subsequent reaction, preferably using a C2-C4 olefin to remove residual Sixe2x80x94H, may be required. The advantage of this process path is that solvent use can be minimized, or in some cases eliminated, and the amount of residual by-products is greatly reduced. If more than one olefin is used simultaneously, one must consider whether the hydrosilation rate for each olefin is competitive with the other. If their hydrosilation rates are competitive, then a randomly functionalized copolymer will be obtained. If the olefins"" hydrosilation rates differ, however, then a block type of copolymer can result unless the olefins are added sequentially so as to insure the even distribution of both olefins on to the SiH containing siloxane substrate.
Siloxane composition (VI) contains cyclosiloxanes and may be prepared by methods well known in the art.
Preferably, each of the siloxane compositions (I)-(VI) will be essentially fully condensed, however, depending on the method of manufacture, up to 20 mole percent silanol can be present in siloxane fluids (I)-(IV).
Depending on the range of temperatures required for a particular traction drive system, siloxane compositions (I)-(VI) may each be employed alone as traction fluids or may be blended to form a traction fluid. Other materials can also be added along with the siloxane compositions of this invention including hydrocarbon fluids such as cyclohexane, alkylcyclohexane, bicycloheptane, bicyclooctane, unsaturated and hydrogenated polyisobutylene, and saturated naphthenic oils, and other organosilicone fluids such as described in JP 6-271588, EP 0350125, U.S. Pat. Nos. 4,449,415 and 4,577,523. In addition, additives such as anti-wear agents, anti-oxidation agents, anti-rust agents, anti-foam agents, etc may be added as necessary. Such additives are well known in the art.
In a preferred embodiment of the invention, anti-wear properties of the traction fluid are also improved therefore reducing or eliminating the need for additional anti-wear additives. A method of reducing wear in a traction drive system having at least two relatively rotatable members in a torque transmitting relationship comprising disposing on the tractive surfaces of the members a traction fluid comprising at least one siloxane composition chosen from
(IVa) 0 to 28 mole percent units of formula (R3SiO1/2), 37 to 93 mole percent units of formula (RCH3SiO2/2), and 6 to 56 mole percent units of formula (RSiO3/2) having a viscosity of from 5.0 to 10,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided (a) at least 65 mole percent of the R groups on (RCH3SiO2/2) are independently selected from alkyl groups comprising 5 to 18 carbon atoms, (b) no more than 35 mole percent of the R groups on (RCH3SiO2/2) are independently selected from aryl groups comprising 6 to 18 carbon atoms, and (c) at least one of all R groups which is not methyl is chosen from alkyl groups comprising 7 to 18 carbon atoms and aryl groups comprising 7 to 18 carbon atoms;
(Va) 4 to 33 mole percent units of formula (R3SiO1/2) and 96 to 67 mole percent units of formula (RCH3SiO2/2) having a viscosity of from 1.0 to 50,000 mPaxc2x7s at 40xc2x0 C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided (a) at least 65 mole percent of the R groups on (RCH3SiO2/2) are independently selected from alkyl groups comprising 5 to 18 carbon atoms, (b) no more than 35 mole percent of the R groups on (RCH3SiO2/2) are independently selected from aryl groups comprising 6 to 18 carbon atoms, and (c) at least one of all R groups which is not methyl is chosen from alkyl groups comprising 7 to 18 carbon atoms and aryl groups comprising 7 to 18 carbon atoms; and
(VIa) cyclosiloxanes of formula (RMeSiO2/2)a having a viscosity of from 2.0 to 50,000 mPaxc2x7s at 40xc2x0 C., where a is an integer ranging from 3 to 20, each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided (a) at least 80 mole percent of the R groups on (RMeSiO2/2) are independently selected from alkyl groups comprising 5 to 18 carbon atoms, and (b) no more than 20 mole percent of the R groups on (RMeSiO2/2) are independently selected from aryl groups comprising 6 to 18 carbon atoms.
Preferably, for improved anti-wear properties the traction fluid comprises at least one siloxane composition chosen from (Va) and (VIa). More preferably, the traction fluid comprises (VIa) where (a) at least 80 mole percent of the R groups on (RMeSiO2/2) are independently selected from branched alkyl groups comprising 5 to 18 carbon atoms, and cyclic alkyl groups comprising 5 to 18 carbon atoms provided no more than 30 mole percent of the R groups on (RMeSiO2/2) are cyclic alkyl groups.
The siloxane compositions of the present invention are useful as traction fluids in traction drive apparatus or friction drive apparatus using rolling contact subject to varied operating temperatures and pressures. Examples of where such traction drive apparatus may be used include automobiles, industrial machinery, and helicopters.